This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Certain abbreviations that may be found in the description and/or in the Figures are herewith defined as follows:    ACK acknowledgement    BLEP block error probability    CCA clear channel assessment    CQI channel quality indicator    CSI channel state information    DTX discontinuous transmission    ECCA extended CCA    HARQ hybrid automatic repeat request    LA link adaptation    LAA license assisted access    LBT listen-before-talk    LTE long term evolution    MAC medium access control    MCS modulation and coding scheme    NACK negative acknowledgement    OLLA outer-loop link adaptation    PDCP packet data convergence protocol    PDCCH physical downlink control channel    PER packet error rate    PHY physical layer (layer 1, L1)    RLC radio link control    RRC radio resource control    SINR signal-to-interference-plus-noise ratio    TTI transmission time interval    TX transmission    TxOP transmission opportunity    UE user equipment
License-Assisted Access (LAA) allowing LTE to be deployed in unlicensed spectrum is a promising approach and currently being specified in 3GPP LTE to meet the ever increasing demand for mobile data traffic. To guarantee peaceful co-existence of LAA using LTE with the incumbent systems such as WiFi, listen-before-talk (LBT) which requires the node to sense the medium before data transmission was introduced.
Listen before Talk (LBT) (or sometimes called Listen before Transmit) is a technique used whereby a radio transmitter first senses its radio environment before it starts a transmission. LBT can be used by a radio device to find a free radio channel or a resource free to operate on. For the LBT technique an LAA node compares the received wideband interference on shared medium against some predefined threshold value (a.k.a. sensing threshold, e.g., −72 dBm), and if the received interference is below the sensing threshold, data transmission is allowed. Hence, the utilization of LBT in LAA nodes implies that the received interference level can be significantly reduced compared to case without LBT usage.
Unfortunately collisions (=overlapping transmissions causing received interference to exceed the used sensing threshold) cannot be fully avoided even with LBT, as the ECCA counter utilized by LBT can reach zero value in the same clear channel assessment (CCA) slot for more than two LAA nodes doing sensing, implying that both LAA nodes are starting a transmission opportunity (TxOP) effectively at the same time. As the utilization of the LBT reduces the received interference at the UE significantly, the impact of possible collision is very dramatic to the received signal quality, e.g., SINR/CSI can easily drop 10-20 dB. As the duration of the collisions is rather short (Cat4 LBT limits the TxOP duration typically to 2-10 ms), collisions cause short and high interference peaks to a received signal quality.
LTE utilizes outer-loop link adaptation (OLLA) algorithm to compensate the impact of imperfections in UE's channel quality indicator (CQI) reports for example. OLLA compensated CQI values are used at eNB for link adaptation (LA) and packet scheduling (PS). It is well known that outer-loop link adaptation performs very well in slowly varying channel conditions, but when received interference fluctuates rapidly performance of the OLLA may be significantly deteriorated. This can be because the OLLA algorithm is not able to provide adaptation fast enough, and the BLEP target towards which OLLA tries to converge cannot be met. Therefore, in LAA using LTE the outer-loop link adaptation (OLLA) can be biased due to collisions of transmissions from other LAA cells (or e.g., WLAN).
Some of the example embodiments of the invention provide at least a novel method and apparatus to, for example, improve an accuracy of OLLA, such as in a case of LAA.